panel/popover: Add grab support, improve placement on screen

The popover will now grab the cursor, ensuring it will be hidden
again should the user click outside of the popover. Keyboard grabs
are not yet implemented.
panel/applets: Update menu applet and window to new popover API
panel/popover: Ensure we disappear when we're supposed to

We now disappear when the user hits ESCAPE, or indeed when we lose focus,
as well as when an area outside of bounds is clicked.
panel/icontasklist: Respond to TOUCH_END "clicks"
Make non-fork status more obvious.
panel/popover: Fix dodgy rx maths

This ensures the left-most and right-most positions for a tail look sane.
panel/popover: Handle both touch and button events
panel: Fix sizing, repaint on resize
Migrate to GLib resources for panel styling

We now build the .css files directly into the resulting budgie-panel
binary, and load them as resources at runtime. This will make it far
easier to maintain the styles, as opposed to defining them in the
header file
data: Fixes for make distcheck
applets/power: Fix icon for fully charged status
applets/power: Fix icon representation of "good" battery

This commit will now show "full" anywhere over 75%, and "good"  between
35% and 75%, giving a more realistic representation of battery status.
panel/icontasklist: Show action menus on right click

When right clicking on an icon in our tasklist, we now show a WnckActionMenu
which supports all possible operations for the window, including minimize,
maximize, close, etc.

In the future, this will probably be wrapped up or reimplemented within
a BudgiePopover to ensure consistency of menu appearance.
Release 1.19
wm: Enable Mutter's edge-tiling by default

In the same way that GNOME Shell overrides Mutters default settings,
budgie-wm now override the edge-tiling schema, enabling edge tiling
by default, controllable via the budgie-wm GSettings.